The main goal of this project is to determine if cell turnover and cell size are reliable biomarkers of aging in mice. Normal aging mice, calorically deprived (CD) mice, and transgenic mice ectopically expressing growth hormone (GH) will be tested. The biomarkers will be divided into lethal determinations on sacrificed animals and a set of nonlethal tests that will be used to predict the longevity of individual mice. The mice to be tested (3-, 12-, 21-, and 30-month-old animals) will be received from the NIA aging study breeding colony (with the exception of the GH mice). The biomarker indices would be expected to correlate to the age of the control mice, and any age-related changes should be slowed in the long-lived CD mice. The GH mice appear to be aging somewhat more rapidly than their controls and thus offer an interesting test of the biomarkers system. Determinations of cell turnover and volume will be carried out both in vivo and in vitro: In vivo--Control and CD mice of 4 age groups will be infused for 1 or 4 weeks with BrdU via subcutaneous osmotic minipumps. At the end of this time, the present of cell turnover in several organs of known high and low mitotic rates will be determined. Determination will be made by nuclear staining with a peroxidase- tagged BrdU antiserum and automated image analysis counting, allowing the rapid processing of counts. The helper and suppressor T cells and the B cells of peripheral blood will be determined for number and history of cell cycling with the aid of a laser-activated cell sorter and specific antisera. In vitro-- Cell populations from those tissues in which cells are dispersible will be placed in culture for determination of clone size distribution for each sample of cells from dermal skin, aortic smooth muscle, and bone marrow fibroblasts. The cell volume of the dissociated cell will also be determined on a FACS analyzer. Only viable cells which stain as diploid with Hoechst 33342 will be included in the volume analysis.